The field of the invention is enclosures for electrical equipment, and particularly, enclosures which seal electrical equipment from the surrounding environment.
There are numerous applications where electrical devices such as switches, relays and terminal blocks must be sealed off from the surrounding environment. Such seals may, for example, exclude liquids such as water where the equipment is exposed to the weather or it may inhibit the passage of gases where the equipment is exposed to volatile vapors. Standards have been established for seals of various types and it is, of course, an objective in the art to meet these standards with any proposed structure.
Standards for sealed enclosures may take the form of specific structural requirements or they may take the form of performance requirements. One such structural standard requires that the juncture between two parts of an enclosure be formed by metal against metal, with the metal having a specified width. On the other hand, to meet certain performance standards it has been found that rings of elastomeric material must be used at the junction of two enclosure parts.
Although prior enclosures are typically designed to meet a specific standard, there are some enclosures available which meet more than one standard. For example, there is described in U.S. Pat. No. 4,158,757, which is commonly assigned, an enclosure seal which includes a metal frame which is clamped between sealing surfaces on an enclosure base and the enclosure cover. Another type of such enclosure, for example, provides a metal flange at the juncture of its base and cover with a rubber O-ring clamped between the mating flange surfaces. In seals of the latter type, it is common to provide grooves in each flange surface to receive the O-ring. This is disadvantageous as two such grooves must be provided. In addition, the O-ring must be aligned with the opposing grooves and this can cause both an installation and sealing problem.